This invention relates to a method of detecting a deflated tire on a vehicle and provides a system suitable for cars and trucks and the like.
European Patent Publication No. 291217 describes a system primarily aimed at vehicles having electronic anti-lock braking systems which use for each wheel a signal generator which gives a multiple signal. The deflation warning system in the European Patent Publication is an add-on system.
In our co-pending application filed the same day as this case, a deflation warning system is described similar to that in the above European Patent Publication. However, the system in the co-pending application uses a single pulse angular velocity measuring system for each wheel. In the single pulse system each wheel has a simple generator which gives a single pulse each time the wheel completes a rotation and the angular velocity is derived by timing the distance between successive pulses. This system has some advantages over the multi-pulse system of European Publication 291217.
Both systems however have disadvantages. In the case of the multi-pulse system already published, the system only works satisfactorily above a certain threshold speed which is determined primarily by the number of pulses per revolution of each wheel and the overall accuracy or smoothness of the signal from the wheel speed generators. The latter system overcomes this low speed threshold but has limitations in higher speed sensitivity due to the computer power necessary to deal with the very short times involved. The latter case provides a first solution to this sensitivity problem by changing the rate at which the reference clock for the timing operates at high speeds, but this first solution is not fully adequate to overcome all conditions of use particularly for very high speed vehicles where both high and low speed sensitivity is required. Furthermore the detection speed of the two systems, i.e. the delay from the time when a tire pressure reaches the threshold and the time when a warning is given, varies at different speeds of the vehicle and so it is not possible with one of the systems alone to give the most efficient combination.